Controlled traction cartridge and differential for a hydrostatic transmission

ABSTRACT

An integrated hydrostatic transaxle including a housing in which is mounted a hydrostatic transmission having a hydraulic pump unit and a hydraulic motor unit with a motor shaft drivingly connected thereto. A differential assembly is drivingly linked to the motor shaft and is used to drive output axle shafts of the transaxle. The differential assembly includes a rotatable gear which is maintained in frictional engagement with at least one bearing surface for frictionally inhibiting the rotational movement thereof.

CROSS REFERENCE OF RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 09/334,050 filedJun. 15, 1999; now, U.S. Pat. No. 6,152,846, which is a continuation ofU.S. Ser. No. 09/104,868, filed Jun. 25, 1998, now U.S. Pat. No.5,984,822; which is a continuation of U.S. Ser. No. 09/698,650 filedAug. 16, 1996, now U.S. Pat. No. 5,897,452.

FIELD OF THE INVENTION

This invention relates generally to transaxles and, more particularly,relates to a controlled traction cartridge for use in providing acontrolled traction differential.

As is known, the use of a standard differential assembly in thetransmission system of a motor vehicle allows the wheels to spin atdifferent speeds. In the case of a vehicle traveling in a straight line,the axle shafts connected to the standard differential assembly willrotate at the same speed. However, when a turn or curve is encountered,the axle shaft nearest the inside of the turn will slow in rotationalspeed while the outer axle shaft will simultaneously increases inrotational speed. As such, the wheels, driven by the axle shafts, areprevented from scuffing the surface across which they travel.

While the standard differential assembly serves an important function inthe operation of a transmission system, the standard differential ofsimple construction has difficult operating under certain conditions.For example, when a first one of the drive tires is disposed in wet,muddy, or loose soil conditions, or when the first drive tire has beenpartially or completely removed from contact with the ground, thecoefficient of friction under the first drive tire will be substantiallylower than that associated with the second drive tire. This resultingfrictional imbalance will tend to cause the second drive tires to remainstationary while the first drive tire will spin without moving thevehicle.

To solve the problem of loss of traction in larger transaxle systems, avariety of techniques have been developed to reduce the tendency of thetransaxle to differential. For example, U.S. Pat. No. 3,528,323 toKamlukin, issued Sep. 15, 1970, discloses a means for preventing freespinning of one of the driven shafts of a transaxle without interferingwith the normal differential capability of the transaxle. In particular,the '323 patent discloses the use of a coil spring to outwardly forcethe gears of the differential into engagement with the differentialhousing thereby introducing a frictional force into the assembly whichacts to resist relative rotation of the axle shafts. In this manner, thefrictional force limits the free spinning of one axle shaft while theother remains stationary.

While the friction inducing means disclosed in the '323 patent works forits intended purpose to provide larger transaxles with a controlledtraction differential assembly, the use of coil springs to apply thefrictional force often requires special tools and/or procedures for usein applying the forces necessary to set the springs. These additionaltools and/or procedures undesirably results in increased manufacturingcosts. Therefore, there remains a need for a controlled tractiondifferential assembly which is simpler to construct, can be produced ata lower cost, and which can be readily incorporated into a smallertransaxle such as an integrated hydrostatic transaxle.

As a result of these existing needs, it is an object of the presentinvention to provide an integrated hydrostatic transaxle having acontrolled traction differential assembly which will provide thehydrostatic transaxle with the benefits and advantages which haveaccrued to other types of transaxles that use controlled tractiondifferential assemblies.

It is a further object of the present invention to provide a controlledtraction differential assembly which is cost effective and relativelyeasy to manufacture.

It is still a further object of the present invention to provide acontrolled traction cartridge for use in conveniently converting astandard differential assembly into a controlled traction differentialassembly.

It is yet a further object of the present invention to provide acontrolled traction differential assembly in which the breakdown bias,i.e., the amount of torque required to cause the differential tooperate, may be easily varied.

SUMMARY OF THE INVENTION

In accordance with these objects, an integrated hydrostatic transaxle isprovided. Generally, the transaxle comprises a hydrostatic transmissionincluding a center section on which is supported a hydraulic pump unitand a hydraulic motor unit and a motor shaft drivingly connected to thehydraulic motor unit. A differential assembly is drivingly linked to themotor shaft for use in driving a pair of axle shafts. The differentialassembly comprises a pair of gears rotatable with respect to each otherand a friction inducing means for use in frictionally inhibiting themovement of at least one of the pair of gears with respect to the otherof the pair of gears. In this manner the frictional force applied to thegear prevents normal operation of the differential when the drive tiresmounted upon the axle shafts are under conditions of frictionalimbalance.

More specifically, the differential assembly includes a pair of gearsrotatable with respect to each other which are both disposed between aninterior and an exterior bearing surface. The interior and the exteriorsurfaces are compressed against the pair of gears to maintain the gearsin frictional engagement therewith thereby inhibiting the rotationalmovement of the pair of gears with respect to one another. In apreferred embodiment of the invention, the interior bearing surface isprovided by forming at least one shoulder on a cross shaft whichsupports the pair of gears and the exterior bearing surface is providedby a pair of bearing blocks.

A better understanding of the objects, advantages, features, propertiesand relationships of the invention will be obtained from the followingdetailed description and accompanying drawings which set forth anillustrative embodiment and is indicative of the various ways in whichthe principles of the invention may be employed.

In accordance with these objects, the invention resides in a controlledtraction cartridge for use in connection with a differential. Thecartridge generally comprises a shaft, a gear mounted on the shaft androtatable with respect thereto, and an interior bearing surfacesassociated with the shaft. The gear is maintained in frictionalengagement with the interior bearing surface for inhibiting the rotationof the gear.

More specifically, the invention resides in a differential and cartridgefor use therein which comprises a hollow shaft supporting a pair ofinterior bearing surfaces, a pair of bearing blocks carried by theshaft, and a pair of gears mounted on the shaft and rotatable withrespect to each other. The gears are each disposed in frictionalengagement with a corresponding one of the bearing blocks and acorresponding one of the interior bearing surfaces. A nut and boltassembly is disposed through the shaft and is used to maintain thefrictional engagement between the pair of bearing blocks, the pair ofgears, and the pair of interior bearing surfaces.

A better understanding of the objects, advantages, features, propertiesand relationships of the invention will be obtained from the followingdetailed description and accompanying drawings which set forth anillustrative embodiment and is indicative of the various ways in whichthe principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference may be had to thepreferred embodiment shown in the following drawings in which:

FIG. 1 illustrates a sectional side view of an integrated hydrostatictransaxle having a controlled traction differential assembly inaccordance with the present invention;

FIG. 2 illustrates a partial sectional bottom plan view of theintegrated hydrostatic transaxle taken along line II—II in FIG. 1;

FIG. 3 illustrates a sectional side view of the integrated hydrostatictransaxle taken along line III—III in FIG. 1;

FIG. 4 illustrates a close-up view of the controlled tractiondifferential assembly as illustrated in FIG. 1;

FIG. 5 illustrates a close-up view of the controlled tractiondifferential assembly as illustrated in FIG. 2;

FIG. 6 illustrates an isometric view of the controlled tractiondifferential cartridge used in connection with the invention asillustrated in FIGS. 1-5; and

FIG. 7 illustrates a sectional side view of the assembled controlledtraction differential cartridge as illustrated in FIG. 6.

DETAILED DESCRIPTION

While the invention can be used in connection with most types oftransaxles it will be described hereinafter in the context of anintegrated hydrostatic transaxle (“IHT”) as the preferred embodimentthereof.

Referring now to the figures, wherein like reference numerals refer tolike elements, there is generally illustrated an IHT 10. While a briefdescription of the general construction and operation of the IHT willfollow, the reader is referred to U.S. Pat. Nos. 5,201,692 and5,314,387, which patents are hereby incorporated by reference in theirentirety, for a more thorough discussion of this subject matter.

As illustrated, the IHT 10 is encased within a housing comprised of afirst housing section 12 and a second housing section 14 joined along asubstantially horizontal split line 16. It is to be understood, however,that the IHT described hereinafter may be disposed within a housingcomprised of any number of housing sections having split lines invarious orientations. Accordingly, the design of the housing illustratedis not meant to be limiting.

The IHT 10 includes a center section 18 having hydraulic porting formedtherein on which are mounted a hydraulic pump unit 20 and a hydraulicmotor unit 22. The particular arrangement of the center section 18,hydraulic pump unit 20, and hydraulic motor unit 22 may be variedaccording to space requirements dictated by the size and configurationof the vehicle with which said IMT is to be employed. Specifically, thehydraulic pump unit 20 generally comprises a pump cylinder block 24having a plurality of piston receiving chambers 26 each of which movablycontains a pump piston 28 and piston spring 30. similarly, the hydraulicmotor unit generally comprises a motor cylinder block 32 having aplurality of piston receiving chambers 34 each of which movably containsa motor piston 36 and piston spring 38. The hydraulic pump unit 20 ishydraulically connected to the hydraulic motor unit 22 through thehydraulic porting formed in the center section 18.

An input shaft 40, which is driven by the engine of the vehicle (notshown), is drivingly connected to the hydraulic pump unit 20 such thatthe rotation of the input shaft 40 rotates the pump cylinder block 24therewith. The rotation of the pump cylinder 24 causes the pump pistons28 to travel up and down as they travel against a swash plate 42. Theswash plate 42 may be moved to a variety of positions to vary the strokeof pump pistons 28; this varies the volume of hydraulic fluid pumpedinto the hydraulic porting which, in turn, ultimately varies the speedof the hydraulic motor unit 22. Specifically, each motor piston 36 isdriven by the pumped hydraulic fluid against a fixed, angularly orientedmotor thrust bearing 44 such that the action of the motor pistons 36against the thrust bearing 44 creates a rotational movement of the motorcylinder block 32. Drivingly connected to the motor cylinder block 32 isa motor shaft 46 which accordingly rotates therewith. a disc brakeassembly 47 is also provided and connected to the motor shaft 46.

In the illustrated embodiment, the motor shaft 46 drives a first gear 48that is drivingly connected to a second reduction gear 50. The reductiongear 50 is drivingly connected to a third, bull gear 52. The bull gear52 imparts the rotational movement translated through the first andsecond gears from the motor shaft 46 to the differential assembly 54. Itis to be understood, however, that the gear configurations describedherein are meant to be illustrative only and that other variations maybe employed without departing from the scope of the invention, e.g., thefirst gear 48 may be arranged to directly drive the bull gear 52 or maybe adapted to drive additional gears for the purpose of providingfurther reduction.

As best seen in FIGS. 4 and 5, the differential assembly 54 generallycomprises a pair of bevel planet gears 56 matingly engaged with the bullgear 52 and, accordingly, rotatable therewith. The bevel planet gears 56are also drivingly connected to a pair of bevel drive gears 58 whichare, in turn, drivingly attached to a pair of oppositely disposed axleshafts 60 which comprise the axle. Specifically, the bevel planet gears56 are engaged with the bull gear 52 through the use of bearing blocks62 which are received in corresponding mating slots formed therewithin.While the preferred embodiment has been illustrated as utilizing twopairs of bevel gears, it will be appreciated by those of ordinary skillin the art that other gearing arrangements may be utilized.

Turning to FIGS. 6 and 7, the bevel planet gears 56 and bearing blocks62 comprise a part of the controlled traction cartridge 64. Morespecifically, the controlled traction cartridge 64 comprises a shaft 66which may be a cross shaft, split shaft, or the like. For ease ofunderstanding the shaft 66 shall be simply referred to herein as crossshaft 66. The cross shaft 66 has an axial opening therethrough and apair of oppositely disposed interior bearing surfaces 68 which may beshoulders formed on the cross shaft 66, retaining rings, or the like.Against the bearing surfaces 68 the bevel planet gears 56 are rotatinglymounted. Additionally, the bearing blocks 62 are also mounted on thecross shaft 66 in communication with the bevel plant gears 56 andprovide an exterior bearing surface 67. In the embodiment shown in FIGS.6 and 7, the exterior bearing surface 67 is generally rectangular inshape and includes two raised opposing exterior bearing surfaces 67 aand 67 b spaced apart and preferably on opposite sides of the shaft 66,i.e., the shaft 66 is between the two raised bearing surfaces 67 a and67 b. Preferably, the ends of the cross shaft 66 are provided with flats70 which engage a corresponding interior surface provided to the bearingblocks 62 to prevent the rotation of the cross shaft 66 with respectthereto. In further embodiments, the flats 70 could be replaced by aspline, serrations, or other like type of rotation resistant features.The prevention of the rotation of the cross shaft 66 is preferred sinceit is seen to maximize the force required to rotate the bevel gears withrespect to one another. In addition, each of the bearing blocks 62 isprovided with a cavity 72 in which is disposed one or more hemisphericalspring washers 74.

To maintain the arrangement of the components of the controlled tractioncartridge 64 a bolt 76 is utilized. Specifically, the bolt 76 ispositioned generally through the center of the above-describedcomponents and a nut 78 is affixed thereto which nut 78 is trapped inthe cavity 72 in the corresponding bearing block 62. Preferably, thecavity 72 in the corresponding bearing block 62 is adapted to preventthe nut 78 from rotating with respect thereto during assembly whileallowing room for the positioning of the spring washers 74 therewithin.To maintain the arrangement of components during operation, it isfurther preferred that the nut 78 be tacked welded to the bolt 76.

When the controlled traction cartridge 64 is fully assembled, the bolt76 and nut 78 function to compress the spring washers 74 within thecavities 72 of the bearing blocks 62. Thereafter, the action of thespring washers 74 against this compressive force drives the bearingblocks 62 into increased frictional engagement with the bevel planetgears 56 which are, in turn, also driven into further frictionalengagement with the shoulders 68 of the cross shaft 66. This frictionalengagement of the bevel planet gears 56 between the bearing blocks 62and the shoulders 68 functions to inhibit the normal rotational movementof the bevel planet gears 56 which occurs when the transaxledifferentials. Specifically, the bevel planet gears 56 will not rotateor differential until the rotational force or torque imparted thereuponby the bevel drive gears 58 is sufficient to overcome the frictionalforces created by engagement of the bevel planet gears 56 with thebearing blocks 62 and shoulders 68. In this manner, when one of thedrive wheels connected to one of the axle shafts is operating in acondition of reduced friction, the herein described controlleddifferential assembly will maintain both drive wheels in uniformrotation until such time as the torque created by the drive wheels issufficient to overcome the frictional forces applied to the bevel planetgears 56. Furthermore the amount of torque required to rotate the bevelplanet gears 56 of the differential assembly, the breakdown bias, may beeasily adjusted by varying the quantity of spring washers utilized or byusing spring washers with different spring constants. Additionally,other components capable of creating similar forces upon the bevelplanet gears in the arrangement above-described may be utilized such swave washers, split washers, or the like.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. For example, thearrangement disclosed herein may be modified whereby the frictionalforce is applied to only one of the bevel planet gears. In this mannercontrolled traction may still be achieved. Accordingly, the particulararrangements disclosed are meant to be illustrative only and notlimiting as to the scope of the invention which is to be given the fullbreadth of the appended claims and any equivalent thereof.

What is claimed is:
 1. A hydrostatic transaxle comprising: a housing; ahydrostatic transmission mounted in said housing including a hydraulicpump unit and a motor unit; a motor shaft drivingly connected to saidhydraulic motor unit; a differential assembly drivingly connected tosaid motor shaft and comprising a first bevel gear restrictivelyrotatably positioned between a first interior bearing surface and afirst exterior bearing surface, wherein the first exterior bearingsurface is axially compressed toward the first interior bearing surface;a first biasing mechanism for axially compressing the first exteriorbearing surface toward the first interior bearing surface; a secondbevel gear restrictively rotatably positioned between a second interiorbearing surface and a second exterior bearing surface, wherein thesecond exterior bearing surface is axially compressed toward the secondinterior bearing surface; and a second biasing mechanism for axiallycompressing the second exterior bearing surface toward the secondexterior bearing surface; and a pair of axle shafts drivingly engaged tosaid differential assembly.
 2. The transaxle of claim 1, wherein saidfirst and second biasing mechanism comprise springs.
 3. A hydrostatictransaxle including a drive axle comprising: a housing having ahydraulic pump and motor mounted therein; a motor shaft connected to thehydraulic motor; a differential comprising a bull gear connected to themotor shaft and a controlled traction cartridge, said controlledtraction cartridge comprising a shaft in the plane perpendicular to thedrive axle, a gear mounted on the shaft, and a friction member mountedon the shaft and rotatably fixed relative to the shaft, wherein thefriction member matingly engages the bull gear.
 4. The transaxle ofclaim 3, wherein said friction member comprises a bearing block.
 5. Thetransaxle of claim 4, wherein said friction member has an exteriorsurface which is generally rectangular in shape, the exterior surfaceincluding two raised bearing surfaces.
 6. The transaxle of claim 4,wherein the cartridge comprises an interior bearing surface associatedwith the shaft and said gear is compressed between said bearing blockand said interior bearing surface.
 7. The transaxle of claim 3, whereinthe cartridge further comprises a spring axially aligned with the shaft,wherein the spring is positioned to apply force to the gear.
 8. Thetransaxle of claim 7, wherein the friction member is translatable alongthe shaft, wherein the cartridge comprises an interior bearing surfacepositioned along the shaft, and wherein the gear is positioned betweenthe friction member and the interior bearing surface.
 9. The transaxleof claim 8, wherein the interior bearing surface is fixed relative tothe shaft.
 10. The transaxle of claim 8, wherein the interior bearingsurface comprises shoulders formed on the shaft.
 11. The transaxle ofclaim 3, further comprising an input shaft engaged to said pump, whereinsaid motor shaft is mounted generally perpendicular to said input shaft,and said pump and motor are mounted on a center section.
 12. Ahydrostatic transaxle for a vehicle having an engine comprising ahousing; a hydrostatic transmission mounted in said housing andcomprising a pump and a motor mounted on a center section, wherein saidpump is driven by an input shaft; a motor shaft drivingly engaged tosaid hydrostatic transmission, wherein said motor shaft is mountedgenerally perpendicular to said input shaft; and a differential assemblycomprising a shaft, a gear rotatably mounted on said shaft, a frictionmember movable along said shaft, an interior bearing surface againstwhich said gear is forced by said friction member whereby the rotationof said gear is frictionally inhibited, and a spring positioned to forcesaid friction member toward said gear.
 13. The transaxle of claim 12,wherein said friction member has an exterior surface which is generallyrectangular in shape, the exterior surface including two raised bearingsurfaces.